Porphyromonas gingivalis (P. gingivalis), an oral anaerobic bacterium, has been implicated as a causative agent of adult type periodontitis. As an asaccharolytic organism, P. gingivalis is totally dependent on external sources of peptides that are necessary for its growth and proliferation. In order to fulfill such a fastidious nutritional requirement this bacterium evolved a complex system of proteolytic enzymes which are now recognized as important virulence factors in the development of periodontal disease (Travis et al., J. Adv. Exp. Med. Biol., 477:455-65 (2000)). The best known and well characterized enzymes of this system are gingipains R and K, arginine and lysine specific, cysteine proteinases (Curtis et al., J. Periodontal Res., 34:464-72 (1999)). Working in concert with the proteinases periodontain (Nelson et al., J. Biol. Chem., 274:12245-51 (1999)), collagenases/gelatinases (Birkedal-Hansen et al., J. Periodontal Res., 23:258-64 (1988); Lawson et al., Infect. Immun., 60:1524-29 (1992); Kato et al., J. Bacteriol., 174:3889-95 (1992), prtT (Otogoto et al., Infect. Immun., 61:117-23 (1993)), and Tpr (Bourgeau et al., Infect. Immun., 60:3186-92 (1992)) as well as host proteinases, this array of enzymes has the potential to degrade proteins from both the periodontal ligamentum and surrounding tissues. Their concerted action leads to the formation of a large pool of oligopeptides, which can be further utilized by P. gingivalis and other oral bacteria. However, P. gingivalis cannot transport poly- and oligo-peptides into the cell, even though it has the ability to thrive on dipeptides as a sole source of carbon. This has led to an interest in studying a specialized group of P. gingivalis peptidases capable of hydrolyzing oligopeptides to di- and tripeptides, which can be subsequently metabolized by this periodontopathogen. The purification, characterization and cloning of prolyl tripeptidylpeptidase A (PtpA), an enzyme which liberates tripeptides from the N-terminal regions of substrates containing proline residues in the third position has been previously reported (Banbula et al., J. Biol. Chem., 274:9246-52 (1999)). Dipeptidylpeptidase-IV (DPP-IV), an enzyme with similar specificity, but only dipeptylpeptidase activity, has also been cloned (Kiyama et al., Biochim. Biophys. Acta, 1396:39-46 (1998)), purified, and characterized (Kumagai et al., Infect. Immun., 68:716-24 (2000); Banbula et al., Infect. Immun., 68:1176-82 (2000)). Together with a recently described angiotensinogen-converting enzyme analogue (Awano et al., FEBS Lett., 460:139-44 (1999)) all of these proteases can hydrolyze peptide bonds containing proline residues. In addition, the P. gingivalis genome contains three further putative coding sequences encoding proteinases homologous with dipeptidylpeptidase-IV, although their activities have not yet been identified (Banbula et al., J. Biol. Chem., 274:9246-52 (1999)).